A serious problem in industrial water systems, especially in cooling water systems, industrial evaporators, and boilers is the deposition of scale, particularly scale-forming salts such as certain carbonates, hydroxides, silicates and sulfates of cations such as calcium and magnesium from aqueous solutions onto heat transfer surfaces. Much of water used in cooling water systems is supplied by the rivers, lakes, ponds, or the like and contains various amounts of scale-forming salts. In cooling tower systems, the cooling effect is achieved by evaporation of a portion of the circulating water in passing over the tower. Because of the evaporation which takes place in cooling, the solids in the water become concentrated. Moreover, because of the inverse solubility of calcium carbonate, calcium sulfate and other hardness salts, the problem of the formation of water-insoluble scales on the heat transfer surfaces is intensified.
Various organic phosphonates have been considered for use in scale control. U.S. Pat. No. 3,336,221 discloses a method of inhibiting the precipitation of scale-forming salts in an aqueous system comprising adding to said system compounds having a methylphosphonic acid bonded to a nitrogen atom such as amino tri (methylphosphonic acid). U.S. Pat No. 3,214,454 teaches use of certain acylation products of phophorous acid (e.g. hydroxyethylidene diphosphonic acid) for scale control. Unfortunately, various phosphonates including amino tri(methylphosphonic acid) and hydroxyethylidene diphosphonic acid are very sensitive to calcium hardness and prone to form calcium phosphonate precipitates.
U.S. Pat. No. 3,474,133 discloses that certain organo-phosphono-amine oxide compounds can be prepared by oxidizing organo-phosphono amine with a suitable oxidizing agent. For instance ethanol bis(dihydrogen phosphonomethyl) amine can be reacted with H.sub.2 O.sub.2 to yield ethanol bis(dihydrogen phosphonomethyl) amine oxide (i.e. HOCH.sub.2 CH.sub.2 N(O) (CH.sub.2 PO.sub.3 H.sub.2).sub.2); and tris(dihydrogen phosphonomethyl) amine can be reacted with H.sub.2 O.sub.2 to yield tris(dihydrogen phosphonomethyl) amine oxide (i.e. ON(CH.sub.2 PO.sub.3 H.sub.2).sub.3). It is disclosed that the organo-phosphono amine oxides have utility in practically all fields of organic chemistry wherein their acidic or salt and/or amine oxide properties can be utilized; and the various utilities indicated for the compounds in such fields include utility as sequestering or chelating agents, water treating agents, stabilizers for peroxy compounds and corrosion inhibitors. In particular, the acids and water soluble salts of the tris(phosphono lower alkylidene) amine oxides are reported to exhibit the property of being effective sequestering agents for metal ions in alkaline mediums. For example, the penta sodium salt of tris(dihydrogen phosphonomethyl) amine oxide is reported to sequester calcium ions in alkaline media in over a mole per mole basis. These tri(phosphono lower alkylidene) amine oxide compounds are considered very sensitive to calcium hardness and they are prone to form calcium phosphonate precipitates.
Much recent research has concerned development of organic water treatment agents. Among the organic agents successfully employed for applications involving corrosion or scale control are numerous organic phosphonates. These compounds may generally be used without detrimentally interfering with other conventional water treatment additives. Phosphonic acid compounds have also been used in other fields for such purposes as flame retardants, plasticizers, lubricants, and surfactants.
U.S. Pat. No. 3,429,914 discloses that certain organo-phosphono-amine oxide compounds can be prepared by oxidizing organo-phosphono amine with a suitable oxidizing agent, and discloses that the organophosphono amine oxides have utility in practically all fields of organic chemistry wherein their acidic or salt and/or amine oxide properties can be utilized. The various utilities indicated for the compounds in such fields include utility as sequestering or chelating agents, water treating agents, stabilizers for peroxy compounds and corrosion inhibitors.
U.S. Pat. No. 4,216,163 discloses certain N-sulfo alkane amino alkane phosphonic acids which can be produced by reacting an alkali metal salt of an amino phosphonic acid with a halo or hydroxyalkane sulfonic acid in an alkaline medium, their high resistance against hydrolysis at high temperatures, their very high water solubility, their suitability as complexing or sequestering agents especially with respect to polyvalent metal ions, and their use in substoichiometric amounts to stabilize the hardness of aqueous media, and their advantageous use for preventing scale and deposit formation in aqueous systems as they are employed for instance in textile bleaching baths, in water used for sterilizing cans, for preventing the formation of resinous deposits in the manufacture of paper, and the like. For example, sodium isothionate is reacted with imino bis-methane phosphonic acid (and sodium hydroxide) to yield N,N-bis-phosphonomethane amino ethane sulfonic acid with a thin-layer chromatogram corresponding to that of the product which is obtained on phosphono methylation of taurine by means of phosphorous acid and formaldehyde.
There is a continuing need for safe and effective water treating agents which can be used to control scale formation or to control corrosion, particularly in systems where substantial calcium is present in the system water.